Paper pickup device in paper feeding cassette

ABSTRACT

There is provided a paper pickup device in a paper feeding cassette having a knock-up plate. In the paper pickup device, a first curved slot is formed on a frontal portion of each sidewall of the paper feeding cassette, a second curved slot is formed above the first slot on one sidewall of the paper feeding cassette, a shaft is protrusively inserted into the first slots from the inside of the paper feeding cassette, a connecting member is rotatably connected to the sidewalls of the paper feeding cassette by hinges, and has a first engaging portion extended upward from a body thereof and a second engaging portion horizontally spaced from the first engaging portion by a predetermined distance and a sub-plate is extended from the connecting member under the knock-up plate, for pressing upward the knock-up plate. A link lever has a spring fixing portion extended downward and a rib extended downward from an end of the link lever, the rib being inserted into the second slot from the sidewall of the paper feeding cassette. A first tension coil spring has one end connected to the first engaging portion and the other end connected to the shaft, for causing the subplate to press upward the knock-up plate, and a second tension coil spring has one end connected to the second engaging portion and the other end connected to the spring fixing portion of the link lever, for adding to the tensile force of the first tension coil spring.

CROSS REFERENCES TO THE RELATED APPLICATIONS AND CLAIM OF PRIORITY

This application is a continuation-in-part application to a co-pendingU.S. patent application Ser. No. 09/168,375 entitled PAPER PICKUP DEVICEIN PAPER FEEDING CASSETTE earlier filed on Oct. 8, 1998 and makesreference to, incorporates the same herein, and claims all benefitsaccruing under 35 U.S.C. §§ 119 and 120. This application makesreference to, incorporates the same herein, and claims all benefitsaccruing under 35 U.S.C. § 119 from an application for PAPER PICKUPDEVICE IN PAPER FEEDING CASSETTE earlier filed in the Korean IndustrialProperty Office on Oct. 8, 1997 and there duly assigned Ser. No.27888/1997, from an application for PAPER PICKUP DEVICE IN PAPER FEEDINGCASSETTE earlier filed in the Korean Industrial Property Office on Nov.3, 1997 and there duly assigned Ser. No. 30916/1997, and from anapplication for PAPER PICKUP DEVICE IN PAPER FEEDING CASSETTE earlierfiled in the Korean Industrial Property Office on Dec. 9, 1997 and thereduly assigned Ser. No. 36232/1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a paper feeding cassette in a laserbeam printer (LBP) using an electrophotographic developing method, andin particular, to a paper pickup device installed to keep plural sheetsof paper in a pickup position.

2. Description of the Related Art

Electrophotographic development is used in printers, copiers, LBPs,facsimile machines and related devices. Such a device is equipped with apaper feeding cassette to accommodate plural sheets of paper, and thepaper feeding cassette has a paper pickup device for keeping the paperpile in a pickup position.

Some examples of paper pickup devices of the conventional art are seen,for example, in the following U.S. patents. U.S. Pat. No. 4,793,606, toYasuoka et al., entitled Paper Feeding Device for A Printer, discloses apaper feeding device for a printer which includes a paper feeding trayand a tray receiver. U.S. Pat. No. 4,830,353, to Hendricks et al.,entitled Device For Holding a Stack of Sheets And Discharging Them FromThe Top Thereof, discloses a device for discharging sheets having aholder for a stack of sheets such that the stack is pressed against aconveyor roller disposed at a fixed location above the holder. U.S. Pat.No. 5,181,713, to Neugebauer, entitled Paper Tray For A Copying Machine,discloses a paper tray arrangement for receiving a stack of paper andwhich is insertable into a receiving device of a copying machine.

A paper pickup device is disclosed in a co-pending U.S. patentapplication Ser. No. 09/168,375 and a description of its structure isincorporated herein. In the mechanism of this device, with a subplateplaced even, a first tension coil spring is strained between a firstengaging portion of a connecting member and a shaft. The strained firsttension coil spring applies a force to move a knock-up plate to a pickupposition. The uppermost paper sheet of a paper pile on the knock-upplate is transferred by rotation of a pickup roller in close contactwith the pickup roller.

Meanwhile, a second tension coil spring is kept stationary, that is, itis not strained. No tensile force is applied to the second tension coilspring because a slot is curved and the distance between a secondengaging portion of the connecting member and an end of a lever is notchanged by rotation of the connecting member around a hinge shaft. As aresult, when the lever end is positioned in a portion of the slot, onlythe first tension coil spring is strained with pickup force, that is,the second tension coil spring is not strained.

When a paper pile is placed with a maximum load on a paper feedingcassette, user manipulation to rotate a locker around a hinge andposition the lever end in the other portion of the slot increases thedistance between the second engaging portion and the lever end Thus, thesecond tension coil spring is strained with a tensile force. That is,the user can freely strain the second tension coil spring by displacingthe lever along the curved slot.

Here, the locker is fixedly positioned by a stopper and the force of thelever and the second tension coil spring In this state, the secondtension coil spring is strained between the lever and the secondengaging portion. It can be concluded that the user can strain thesecond tension coil spring by displacing the lever end along the slotand thus changing the distance between the second engaging portion andthe lever. In addition, the shaft can be selectively positioned in twoportions of a slot, which allows the user to freely adjust applicationof a paper pickup force along with the movement of the shaft.

However, the above paper pickup device suffers from the disadvantagesthat assembly is difficult and reliability of parts is decreased due toa large part tolerance involved in designing caused by requirement formany parts.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved paper pickup device for a laser beam printer.

It is also an object of the present invention to provide a paper pickupdevice which enables papers of different sizes and weights to bereliably picked up.

It is another object of the invention to provide a paper pickup devicewhich requires fewer parts than existing paper pickup devices.

It is still another object of the present invention to provide a paperpickup device which has a reduced part tolerance.

It is yet another object of the present invention to provide a paperpickup device which has improved reliability.

It is a further object of the present invention to provide a paperpickup device which is easier to assemble.

It is a still further object of the present invention to provide a paperpickup device which is less expensive.

To achieve these and other objects, there is provided a paper pickupdevice in a paper feeding cassette having a knock-up plate. In the paperpickup device, a first curved slot is formed on a frontal portion ofeach sidewall of the paper feeding cassette, a second curved slot isformed above the first slot on one sidewall of the paper feedingcassette, a shaft is protrusively inserted into the first slots from theinside of the paper feeding cassette, a connecting member is rotatablyconnected to the sidewalls of the paper feeding cassette by hinges, andhas a first engaging portion extended upward from a body thereof and asecond engaging portion horizontally spaced from the first engagingportion by a predetermined distance, and a sub-plate is extended fromthe connecting member under the knock-up plate, for pressing theknock-up plate upward. A link lever has a spring fixing portion extendeddownward and a rib extended downward from an end of the link lever, therib being inserted into the second slot from the sidewall of the paperfeeding cassette. A first tension coil spring has one end connected tothe first engaging portion and the other end connected to the shaft, forcausing the subplate to press upward the knock-up plate, and a secondtension coil spring has one end connected to the second engaging portionand the other end connected to the spring fixing portion of the linklever, for adding to the tensile force of the first tension coil spring.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail a preferred embodiment thereofwith reference to the attached drawings in which:

FIG. 1 is a schematic view of a paper pickup device with a tensile forceapplied to a first tension coil spring;

FIG. 2 is a schematic view of the paper pickup device of FIG. 1, withtensile force applied to both the first and second tension coil springs;

FIG. 3 is a schematic perspective view of a paper pickup deviceaccording to a preferred embodiment of the present invention;

FIG. 4 is a partial perspective view showing the exterior of a paperfeeding cassette having the paper pickup device according to theembodiment of the present invention;

FIG. 5 is a side view of the paper pickup device according to theembodiment of the present invention;

FIG. 6 is a side view of the paper pickup device with tensile forceapplied to a first tension coil spring; and

FIG. 7 is a side view of the paper pickup device with tensile forceapplied to both the first and second tension coil springs.

DETAILED DESCRIPTION OF THE DRAWINGS

A paper pickup device is disclosed in a co-pending U.S. patentapplication Ser. No. 09/168,375 and a description of its structure isincorporated herein. In the mechanism of the above device, with subplate110 placed even, first tension coil spring 150 is strained between firstengaging portion 111 of a connecting member and shaft 120, as shown inFIGS. 1 and 2. The strained first tension coil spring 150 applies aforce to move knock-up plate 101 to a pickup position. The uppermostpaper sheet of a paper pile on knock-up plate 101 is transferred byrotation of a pickup roller (not shown) in close contact with the pickuproller.

Meanwhile, second tension coil spring 160 is kept stationary, that is,not strained. No tensile force is applied to second tension coil spring160 because slot 103 is curved and the distance between second engagingportion 112 of the connecting member and end 140 of a lever is notchanged in spite of rotation of the connecting member around a hingeshaft. As a result, when lever end 140 is positioned in a portion ofslot 103, only first tension coil spring 150 is strained with pickupforce, that is, second tension coil spring 160 is not strained.

As shown in FIG. 2, when a paper pile is placed with a maximum load onpaper feeding cassette 100, user manipulation to rotate locker 130around a hinge and position lever end 140 in the other portion of slot103 increases the distance between second engaging portion 112 and leverend 140. Thus, second tension coil spring 160 is strained with a tensileforce. That is, the user can freely strain second tension coil spring160 by displacing the lever along curved slot 103.

Here, locker 130 is fixedly positioned by stopper 131 and the force ofthe lever and second tension coil spring 160. In this state, secondtension coil spring 160 is strained between the lever and secondengaging portion 112. It can be concluded that the user can strainsecond tension coil spring 160 by displacing lever end 140 along slot103, thus changing the distance between second engaging portion 112 andthe lever. In addition, shaft 120 is selectively positioned in twoportions of slot 102, which allows the user to freely adjust applicationof a paper pickup force along with the movement of shaft 120.

A detailed description of a preferred embodiment of the presentinvention will hereinbelow be given with reference to the attacheddrawings. It is to be noted that like reference numerals denote the samecomponents in the drawings and a detailed description of a known relatedfunction or structure of the present invention is omitted if it isdeemed to obscure the subject matter of the present invention.

FIG. 3 is a schematic perspective view of a paper pickup deviceaccording to a preferred embodiment of the present invention, and FIG. 4is a partial perspective view showing the exterior of a paper feedingcassette having the paper pickup device. Referring to FIGS. 3 and 4,first curved slot 11 is formed on a frontal portion of each side wall ofpaper feeding cassette 10 to protrusively insert shaft 30 thereinto.Second curved slot 12 is formed just above first slot 11 on one sidewallof paper feeding cassette 10. Iinsertion hole 13 is formed at one sideof second slot 12. First slot 11 gets wider in a lower portion thereofso as to keep shaft 30 in position.

Under knock-up plate 14 of paper feeding cassette 10 is placed subplate20 for pressing upward knock-up plate 10. Subplate 20 is rotatablyconnected to the sidewalls of paper feeding cassette 10 by hinges 24through connecting member 21. Connecting member 21 has first engagingportion 22 extended upward from the body thereof and second engagingportion 23 horizontally spaced from first engaging portion 22 by apredetermined distance.

Shaft-shaped link lever 40 is prepared to be inserted into second slot12. Spring fixing portion 41 is extended downward from link lever 40,and rib 42 is extended downward from an end of link lever 40 to beinserted into second slot 12 from the sidewall of paper feeding cassette10. Rib 42 has protrusion 42a on the inner surface to be inserted intoinsertion hole 13, for keeping link lever 40 in position. Knob 42b isformed on the outer surface of rib 42 perpendicularly to the outersurface, for facilitating user manipulation of link lever 40.

Then, first tension coil spring 50 connects first engaging portion 22 toshaft 30, for causing subplate 20 to press up knock-up plate 14. Secondtension coil spring 60 connects second engaging portion 23 to springfixing portion 41 of link lever 40, for adding to the tensile force offirst tension coil spring 50. A plurality of rollers 25 are provided inan area where subplate 20 contacts knock-up plate 14 to make contactwith the lower surface of knock-up plate 14.

FIG. 5 is a side view of the paper pickup device according to theembodiment of the present invention, FIG. 6 is a side view of the paperpickup device with tensile force applied to the first tension coilspring, and FIG. 7 is a side view of the paper pickup device withtensile force applied to both the first and second tension coil springs.Referring to FIG. 5, shaft 30 is positioned in an upper portion of firstslot 11 and link lever 40 can make a free movement along second slot 12.In this state, subplate 20 applies a minimum upward pressure to knock-upplate 14.

Referring to FIG. 6, with user displacement of shaft 30 to lower portion11a of first slot 11, a predetermined tensile force is applied to firsttension coil spring 50 and link lever 40 can move freely along secondslot 12. In this state, since first tension coil spring 50 applies thetensile force to subplate 20, subplate 20 presses upward the knock-upplate 14 with a stronger force than in FIG. 5.

Referring to FIG. 7, with shaft 30 positioned in lower portion 11a offirst slot 11 and protrusion 42a of link lever 40 inserted intoinsertion hole 13 by user manipulation, both first and second tensioncoil springs 50 and 60 are concurrently strained. Since the tensileforce of first and second tension coil springs 50 and 60 issimultaneously applied to subplate 20, subplate 20 presses upwardknock-up plate 14 with a maximum force.

As described above, the present invention is advantageous in thatapplication of tensile force to the subplate can be simply controlled instages with use of just two parts.

While the present invention has been described in detail with referenceto the specific embodiment, it is a mere exemplary application. Thus, itis to be clearly understood that many variations can be made by anyoneskilled in the art within the scope and spirit of the present invention.

What is claimed is:
 1. A paper pickup device for a laser beam printer,comprising:a paper feeding cassette having two sidewalls, each sidewallhaving a first curved slot in a frontal portion of said sidewall andeach sidewall having a second curved slot formed above said first curvedslot; a knock-up plate in the paper feeding cassette; a shaft installedbetween said sidewalls of said paper feeding cassette so as to protrudefrom said first curved slots; a connecting member rotatably connected tosaid sidewalls of said paper feeding cassette; a first engaging portionextending upward from said connecting member; a second engaging portionconnected to and horizontally spaced from said first engaging portion; asubplate extending from said connecting member, said subplate beingunder said knock-up plate; a link lever which is shaft-shaped, disposedbetween said sidewalls; a spring-fixing portion extending downward fromsaid link lever; a rib extending downward from an end of said linklever, said rib being inserted into said second slot; a first tensioncoil spring having one end connected to said first engaging portion anda second end connected to said shaft so as to press said subplate upwardagainst said knockup plate; and a second tension coil spring having oneend connected to said second engaging portion and the other endconnected to said spring-fixing portion of said link lever so as toadditionally press said subplate upward against said knock-up plate. 2.The paper pickup device of claim 1, further comprised of said firstcurved slot having a first terminal end separated by a length of saidfirst curved slot from a second terminal end with said second terminalend exhibiting a width that is shaped wider than a width exhibited bysaid first curved slot along said length.
 3. The paper pickup device ofclaim 1, further comprising:a sidewall of said paper feeding cassettehaving an insertion hole on one side of said second curved slot; aprotrusion on the inner surface of said rib, said protrusion beinginsertable into said insertion hole.
 4. The paper pickup device of claim1, further comprising:a knob formed on the outer surface of said rib formanipulation of said link lever by a user.
 5. The paper pickup device ofclaim 4, further comprising:said knob extending perpendicular to saidouter surface of said rib.
 6. The paper pickup device of claim 1,further comprising:a roller mounted on said subplate and contacting alower surface of said knock-up plate.
 7. The paper pickup device ofclaim 6, further comprising:a plurality of rollers mounted on saidsubplate and contacting a lower surface of said knock-up plate.